How to Use mb_eregi_replace with trim() to Remove Leading and Trailing Spaces During Replacement

M66 2025-06-23

In PHP, the mb_eregi_replace() function is incredibly useful when handling multi-byte strings. It works similarly to eregi_replace(), but is designed for multi-byte strings such as UTF-8 encoded Chinese text. However, in practical use, we may encounter a common issue: how to remove any unnecessary leading or trailing spaces when using mb_eregi_replace() to replace content?

For example, suppose we want to replace the text [URL]http://m66.net/page[/URL] with an HTML link, ensuring that the replaced result is not affected by any extra spaces around it that could affect the layout or introduce additional spaces. In this case, trim() can come in handy.

Example: Basic Usage

Let's first look at a basic replacement example:


$text = "  Here is a link: [URL]http://m66.net/page[/URL], please click.";  
$pattern = ' $URL$ URL(.*?) $/URL$ /URL';

$replacement = 'link';
$result = mb_eregi_replace($pattern, $replacement, $text);

echo $result;

The output will be:

Here is a link: <a href="http://m66.net/page">link</a>, please click.

At first glance, it seems fine. However, if there are leading or trailing spaces around the content within the [URL] tag, for example:

[URL] http://m66.net/page [/URL]

After replacement, the href attribute in the HTML link will contain unnecessary spaces, potentially causing the link to not open correctly or display abnormally.

Improvement: Using trim() Together

To resolve this issue, we need to use trim() within a callback function. Unfortunately, mb_eregi_replace() does not directly support callback functions. However, we can achieve the same goal by using mb_ereg_replace_callback().

The modified code is as follows:


$text = " Here is a link: [URL] http://m66.net/page [/URL], please click.";  
$pattern = ' $URL$ URL(.*?) $/URL$ /URL';
$result = mb_ereg_replace_callback(

$pattern,

function ($matches) {

$url = trim($matches[1]);

return 'link';

},

$text

);

echo $result;

The output will now be:

Here is a link: <a href="http://m66.net/page">link</a>, please click.

Now, there will be no extra spaces in the link, making the result more robust and professional.

Summary

While mb_eregi_replace() is convenient for performing case-insensitive multi-byte replacements, it does not support passing custom logic like preg_replace_callback() does. To resolve the space issue, the best practice is to use mb_ereg_replace_callback(), allowing for more flexible handling of the match results with functions like trim(). This ensures that the output links or other replacement content are more accurate, robust, and provide a better overall user experience.